The present invention relates to a device and a method for preventing vertical displacements and vertical vibrations of the load carrying means of vertical conveyors while they are stopped at landings, achieving the desired effect by the load carrying means being held fast on its guiderails during landing stops by means of frictional engagement, this frictional engagement being released in the presence of a corresponding control command.
The following description relates to passenger- or freight-elevators that represent a special type of vertical conveyors. The designation of the components therefore corresponds to the technical terms of the elevator field. For example, the load carrying means is designated as elevator car or car.
The European patent 0 346 195 discloses an electromagnetically actuated caliper which is designed inter alia to bind the car or counterweight of an elevator to its respective guiderail by means of frictional engagement. The brake has two double-arm levers with a common joint at their mid-point whose shaft is fastened to the car or counterweight. The gripping arms of the levers are lined with brake linings and embrace the tongue of the guiderail of the car or counterweight. The opposite, driving arms of the levers are held apart by a compression spring which gives rise to the gripping force between the brake linings and the tongue of the guiderail at the other end of the levers. Concentric to the compression spring which pushes the ends apart there is a pull-type electromagnet which, when current flows through it, overcomes the force of the compression spring and thereby opens the brake.
The disclosed braking device is particularly intended as a holding brake for counterweights or cars of elevators driven by linear motors, and the patent claims relate mainly to the embodiment of an integral damping element to prevent switching jolts and switching noises being caused by the pull-type magnet.
In elevator installations with large travel heights, cars hanging on suspension means such as, for example, wire ropes or flat belts have the disadvantage that when stopping at a landing they undergo relatively large vertical displacements whose cause is the stretching or contraction of the elastic suspension means due to changes in load. Such changes in load in the car are caused by passengers entering or leaving, or by transportation equipment being put into or taken out of the car. If the vertical displacements exceed a variable limit value, the drive usually executes a compensating movement until the surfaces of the car floor and landing floor are again at the same level. Depending on the type of change in load, several such compensating procedures may be necessary during a stop at a landing.
Furthermore, while stopped at a landing, such elevator cars are susceptible to vertical vibrations caused by the stopping process, changes in load, or the level-compensating procedures described above. Vertical displacements and vibrations of the car can cause passengers to experience unpleasant sensations or even alarm. Moreover, if the surfaces of the car floor and hoistway door sill are not at exactly the same level, this can lead to accidents caused by passengers stumbling as they enter or leave the car.
The situation described can be improved by holding the elevator car fast on its guiderails by frictional engagement.